Charge transport in high-performance ink-jet printed single-droplet organic transistors based on a silylethynyl substituted pentacene/insulating polymer blend

We present a systematic study of the influence of material composition and ink-jet processing conditions on the charge transport in bottom-gate field-effect transistors based on blends of 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) and polystyrene. After careful process optimizations of blending ratio and printing temperature we routinely can make transistors with an average mobility of 1 cm2/Vs (maximum value 1.5 cm2/Vs), on/off ratio exceeding 10^7, and sharp turn-on in current (sub-threshold slopes approaching 60 mV/decade). These characteristics are superior to the TIPS-PEN only transistors. Using channel scaling measurements and scanning Kelvin probe microscopy, the sharp turn-on in current in the blends is attributed to a contact resistance that originates from a thin insulating layer between the injecting contacts and the semiconductor channel.